JP2009016396A - Wavelength scanning type fiber laser light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength scanning type laser light source which can scan the wavelengths of a light source having a narrow band spectrum in a wide band at a high speed and continuously, wherein the necessary number of optical isolators is reduced and the increase of the noises due to optical losses in the optical isolators is reduced. <P>SOLUTION: This wavelength scanning type fiber laser light source comprises two ring-type resonant Fabry-Perot electro-optical modulators 11A, 11B having nearby FSRs (Free spectral range), an optical path for laser oscillation formed by connecting an optical amplifier 12 having a gain in the oscillation wavelength and an optical cup, etc., 14 from which output light is to be taken out together with an optical fiber, and a resonator length control unit 15 for periodically changing the resonator length of one Fabry-Perot resonator in a fixed range, and consists of a confocal Fabry-Perot electro-optical modulator wherein curvatures of respective concave mirrors are so set that the Fabry-Perot resonator including an electro-optical crystal becomes confocal, and optically modulates the passing light by a periodical scanning signal given by the resonator length control unit 15. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wavelength scanning fiber laser light source that generates monochromatic light and periodically scans its emission wavelength.

  Conventionally, a broadband light source is used as a light source of an analysis apparatus that irradiates a measurement object with light and analyzes the measurement object. In the spectroscopic analysis, there is a wide range of methods for projecting broadband light onto a measurement target and spatially resolving the reflected or transmitted light into wavelength components using a diffraction grating or the like, or performing Fourier transform to frequency components using an interferometer. It is used. Examples of such a light source include a white light source and an ASE light source using erbium-doped fiber (EDF). However, in such spectroscopic analysis, since the light output intensity density with respect to the wavelength is low, the level of light that can be used in spectroscopy is small. For this reason, even if Fourier transform analysis is performed, the detection light signal is buried in noise, which makes it difficult to analyze.

  There is also a method of using a wavelength-variable light source that changes a single spectrum of a strong level in a desired band as a light source of the analyzer. In this method, the wavelength of light having strong single light is changed to irradiate the measurement object, and light that passes through or reflects the measurement object is received by the light receiving element as it is. In this method, since the light intensity density with respect to the wavelength of the light source is high, the detection light level and the signal-to-noise ratio are sufficiently high, and sufficient measurement accuracy can be realized.

  Conventional wavelength tunable light sources include an external resonator type laser, a fiber ring laser, and a type in which a wavelength tunable mechanism is provided in a laser element. An external resonator type laser uses a gain medium, for example, a semiconductor laser. An external resonator is formed between one end face of the semiconductor laser and an external mirror, and the wavelength can be varied by a diffraction grating or the like in the external resonator. By providing a filter, the oscillation wavelength is changed to obtain a wavelength tunable light source.

  In the external resonator type laser light source, the external resonator length is relatively small, for example, 50 mm, and the longitudinal mode interval is, for example, 3 GHz. Therefore, simply changing the wavelength of the tunable filter makes it unstable between the longitudinal modes. For example, discontinuous mode hops may occur between modes, or oscillation may occur in multiple modes. Therefore, in order to continuously change the wavelength in a single mode and stabilize the output, the external resonator length must be delicately controlled using a piezo element or the like, and complicated control is required. . In addition, there is a drawback that it is difficult to change the wavelength at high speed because the wavelength and the external resonator length are controlled in synchronization with the mechanical operation.

  Conventionally, a gain medium and an optical circulator having a gain in an oscillation wavelength in an optical fiber loop as a wavelength scanning type fiber laser light source capable of continuously scanning a wavelength of a light source having a narrow band spectrum in a wide band at high speed. , The light extracted by the optical circulator is magnified by the collimator lens, the polygon mirror provided on the optical axis is rotated, and the light reflected by the polygon mirror is reflected in the same direction as the incident light. A wavelength scanning fiber laser light source having a configuration provided with a diffraction grating having a Littrow configuration has been proposed. In this wavelength scanning fiber laser light source, the selection wavelength changes depending on the incident angle to the diffraction grating, and the selectivity increases by two incidences. Therefore, even if the polygon mirror is rotated at a high speed and the selection wavelength is changed, it is narrow. The oscillation wavelength can be changed in the band (see, for example, Patent Document 1).

  Conventionally, a variable wavelength light source using a ring laser using an erbium-doped fiber has also been proposed. For example, as shown in FIG. 23, the wavelength tunable light source 1000 includes a fiber amplifier 1112 using an erbium-doped fiber (EDF) as a gain medium, and a wavelength tunable bandpass filter 1114 provided in the optical fiber loop 1113. The wavelength of the laser light extracted through the optical coupler 1115 connected to the optical fiber loop 1113 is varied by changing the wavelength of the band pass filter 1114. In this case, since the resonator length of the optical fiber loop 1113 can be increased to, for example, 30 m, the longitudinal mode interval can be reduced. Therefore, the influence of the mode hop can be eliminated without changing the resonator length. Accordingly, although it is not strictly single mode oscillation, it is possible to perform quasi-continuous wavelength tuning only by changing the selected wavelength of the bandpass filter 1114 (see, for example, Non-Patent Document 1).

  Further, in the type in which the wavelength variable mechanism is provided in the laser element, a DBR-LD (Distributed Bragg reflector laser diode) in which an active region that generates gain and a DBR region that generates reflection by a diffraction grating are formed in the same laser element. ) Has been proposed. The wavelength variable range of this DBR-LD is about 10 nm at the maximum. In addition, a DBR-LD using a non-uniform diffraction grating in which an active region that generates a gain and a DBR region sandwiching the active region between the front and the rear is formed in the same laser element has been proposed. In the front and rear DBR regions, a large number of reflection peaks are generated by the non-uniform diffraction grating, and the interval between the reflection peaks is slightly shifted between the front and the rear. With this structure, a so-called “vernier effect” can be obtained, so that an extremely wide wavelength variation is possible. In the DBR-LD using this non-uniform diffraction grating, wavelength variable operation exceeding 100 nm is realized. In the DBR-LD using this non-uniform diffraction grating, a wavelength variable operation exceeding 100 nm and a quasi-continuous wavelength variable operation of 40 nm are realized (for example, see Patent Document 2).

JP 2006-237359 A JP 2006-278770 A YAMASHITA ET AL., IEEE JOURAL ON SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL.7, NO.1 JANUARY / FEBRUARY 2001, PP41 ~ 43

  By the way, when using a wavelength tunable light source as a light source for an analyzer, it is necessary to change the wavelength at high speed and to narrow the width of the oscillation spectrum, and characteristics corresponding to this are also required for the bandpass filter. Is done. For example, when high-speed wavelength scanning becomes available in optical coherence tomography (OCT), dynamic analysis such as high-speed image processing, blood flow observation, and oxygen saturation concentration change can be performed. Is required.

  As a product that employs the disclosed technology of Patent Document 1, for example, Santec Corporation provides a wavelength scanning laser light source HSL-2000 capable of repeatedly scanning a wavelength at a scan rate of a maximum of 20 kHz. However, at present, 20 kHz is only practically used as the wavelength scanning period.

  This requires several seconds to obtain a stereoscopic image by optical coherence tomography (OCT).

  Further, as described in Patent Document 2, in the DBR-LD, by performing carrier injection in the DBR region, the refractive index in this portion is changed to realize the wavelength variable operation. For this reason, if crystal defects grow due to current injection, the rate of change in the refractive index with respect to current injection varies significantly, so that it is difficult to maintain laser oscillation at a stable wavelength over a long period of time. Further, with the current compound semiconductor process technology, an inch-up of 2 inches or more is impossible. For this reason, it is difficult to reduce the price of the laser element that has become complicated and large in size. However, if it is a small element of 1 mm or less, the longitudinal mode interval is large, for example, 100 GHz, and if the wavelength of the tunable filter that changes the wavelength at high speed is simply changed, the wavelength tunable operation is performed every longitudinal mode interval. It becomes. Such a large and discrete wavelength tunable operation is too large for application to optical coherence tomography. Furthermore, if the wavelength of the tunable filter is simply changed, it becomes unstable between the longitudinal modes. For example, discontinuous mode hops may occur between modes, or oscillation may occur in multiple modes.

  Furthermore, the disclosed technique of Patent Document 2 is a configuration in which a plurality of optical resonators are adopted as a wavelength filter by a ring-type optical resonator, and the wavelength can be varied by the vernier effect, but the wavelength can be varied by a heater. Not suitable for high speed scanning. In addition, it is difficult to adjust the resonator lengths of a plurality of ring-type optical resonators on the same substrate. Further, since the entire length of the laser including the ring type optical resonator is short, simply changing the wavelength of the wavelength tunable filter makes it unstable between the longitudinal modes. For example, discontinuous mode hops may occur between modes, or oscillation may occur in multiple modes.

  Therefore, the applicant of the present application shows, for example, a basic configuration as a wavelength scanning type laser light source capable of continuously scanning a wavelength of a light source having a narrow band spectrum at a high speed in a wide band, for example, as shown in FIG. As described above, an optical fiber loop 1011 serving as an optical path for laser oscillation, an optical amplifier 1012 provided in the optical fiber loop 1011 and having a gain at an oscillation wavelength, and an optical fiber loop 1011 provided in the optical fiber loop 1011 and in close proximity to each other. range) two Fabry-Perot resonators 1013A and 1013B, an optical coupler 1014 that is connected to the optical fiber loop 1011 and extracts part of the light passing through the optical fiber loop 1011 and two units having the adjacent FSR At least of Fabry-Perot resonators 1013A and 1013B On the other hand, here, as a Japanese Patent Application No. 2007-18168, a wavelength scanning fiber laser light source 1000 including a resonator length control unit 1015 that periodically changes the resonator length of a Fabry-Perot resonator 1013A within a certain range is disclosed. is suggesting.

  A polarizer is inserted into the loop in order to determine the polarization state of the light passing through the optical fiber loop 1011 serving as the laser oscillation optical path.

  In this wavelength scanning fiber laser light source 1000, the two Fabry-Perot resonators 1013A and 1013B having adjacent FSRs function as wavelength selection filters. In addition, at least one of the two Fabry-Perot resonators 1013A and 1013B, here, the Fabry-Perot resonator 1013A can change the selected wavelength by changing the resonator length.

  The two Fabry-Perot resonators 1013A and 1013B having the adjacent FSRs can change the selected wavelength by the vernier effect by changing the resonator length of one Fabry-Perot resonator 1013A. It functions as a bandpass filter having a wavelength selection characteristic of the band.

  In this wavelength scanning fiber laser light source 1000, the light that has passed through the band-pass filters of the two Fabry-Perot resonators 1013A and 1013B having the FSRs close to each other provided in the optical fiber loop 1011 has gain in the oscillation wavelength. Oscillated by being amplified by the amplifier 1012 and fed back through the optical fiber loop 1011. In this wavelength scanning fiber laser light source 1000, the oscillation wavelength is periodically changed by periodically changing the resonator length of the Fabry-Perot resonator 1013A by a resonator length control unit 1015 within a certain range. The wavelength of the laser light taken out via the optical coupler 1014 changes periodically.

  The optical coupler 14 for extracting laser light from the optical fiber loop 1011 is provided after the optical amplifier 1012. However, the optical coupler 14 is provided before the optical amplifier 1012 or between the two Fabry-Perot resonators 1013A and 1013B. It may be.

  In the wavelength scanning fiber laser light source 100 having such a configuration, the resonator length of the optical fiber loop 1011 can be increased. By setting the resonator length of the optical fiber loop 1011 to, for example, 1000 m, the longitudinal mode interval of the entire laser can be reduced. For example, it can be narrowed to about 200 kHz. As a result, the longitudinal mode interval of the entire laser can be sufficiently narrower than the bandwidth (FSR / finesse, for example, 2.5 GHz / 50 = 50 MHz) of each Fabry-Perot resonator 1013A, 1013B. The effect of mode hop can be eliminated without changing the resonator length. Therefore, although it is not strictly single mode oscillation, it is possible to tune the wavelength continuously in a pseudo manner simply by changing the selected wavelength of the bandpass filter.

  Here, the transmission spectrum of a normal optical resonator is shown in FIGS. The horizontal axis is the frequency of light, normalized as FSR = 1, and indicates a range of 100 × FSR. You can see 100 modes per FSR. FIG. 25B is an enlarged view of FIG.

  26A to 26G show transmission spectra when two optical resonators having different FSRs of 1% are connected in cascade. Each horizontal axis is the same as (A) in FIG. 25. However, since the mode intervals of the two optical resonators are different, the vernier effect is caused, and the envelope of the spectrum formed by the mode with a small FSR is Equivalent to an optical resonator with a large FSR. The difference of 1% FSR makes the FSR of the moire fringe envelope 100 times. It can also be seen that when the resonator length is changed by about the wavelength, the peak changes by the FSR of the moire fringe envelope. A partially enlarged view of FIG. 26 is shown in FIG.

  Therefore, even if an optical resonator having a small FSR is used, if the vernier phenomenon of the spectrum of the two optical resonators is used, the FSR of the Moire fringe envelope is inversely proportional to the difference between the FSRs of the two optical resonators. And get bigger.

  That is, even if an optical resonator having a small FSR is used, a tunable laser light source can be configured by utilizing the vernier phenomenon of the spectrum of two optical resonators.

  In this case, the wavelength of the laser jumps every FSR (for example, 2.5 GHz) at an interval corresponding to the FSR of the two optical resonators. However, in the case of applications such as optical CT, the measurement range in the depth direction is c If the range is sufficiently narrower than / FSR (about 10 cm), it can be regarded as a quasi-continuous variable wavelength.

It is also called a Fabry-Perot electro-optic modulator (or optical comb generator) with a structure in which an electrode is attached to a Fabry-Perot resonator constructed of an electrically variable refractive index material such as LN (LiNbO ₃ ). By using the modulator, the wavelength can be varied by the electro-optic effect. Since it is an electrical modulation, it has excellent linearity and reproducibility.

  Therefore, a Fabry-Perot electro-optic modulator is used as the Fabry-Perot resonator 1013A in which the resonator length in the wavelength scanning fiber laser light source 1000 is variable. Then, a periodic signal such as a sawtooth wave is given to the Fabry-Perot electro-optic modulator by the resonator length control unit 1015 and optically modulated, so that the oscillation wavelength of the wavelength scanning fiber laser light source 1000 can be made with high accuracy. And it can scan at high speed.

  FIG. 28 shows an actual configuration example of a wavelength scanning fiber laser light source 1000 using the Fabry-Perot electro-optic modulators 1013A ′ and 1013B ′ for the two Fabry-Perot resonators 1013A and 1013B.

  Since the currently available Fabry-Perot electro-optic modulator has reflection, isolators 1017A, 1017B, 1017C, and 1017D are inserted in the wavelength scanning fiber laser light source 1000 shown in FIG. A delay line 1018 is inserted. For example, the delay line is a 1 km fiber. As a result, the time for the light to travel around the optical fiber loop 1011 is 5 μs, so that the mode interval is 200 kHz. The entire system of this wavelength scanning fiber laser light source 1000 is constructed with polarization conservation, and a polarizer 1019 is connected to an optical amplifier 1012 and an isolator in order to determine the polarization state of light passing through an optical fiber loop 1011 serving as an optical path for laser oscillation. It is inserted between 1017C. For the delay, a Faraday mirror, an SM fiber, and a PBS coupler can be used. The scanning frequency can be an integer multiple of 200 kHz.

  Here, as the optical amplifier 1012, the Fabry-Perot resonators 1013A 'and 1013B', and the optical coupler 1014 in the wavelength scanning fiber laser light source 1000, an optical fiber amplifier EFDA for wavelength 1.5 μm band, two comb generators The fiber ring laser shown in FIG. 29 is configured by using the modules OFCG1, OFCG2 and the optical coupler PC, and the wavelength variable characteristic by the bias voltage to the comb generator module OFCG1 is measured. It functioned as a light source, and the result as shown in FIG. 30 was obtained.

  However, the wavelength scanning fiber laser light source 2000 configured as described above requires two waveguide-type Fabry-Perot electro-optic modulators 2013A ′ and 2013B ′, and each waveguide-type Fabry-Perot electro-optic modulator 2013A ′, The optical isolators 1017A, 1017B, and 1017C must be provided at the input and output of 2013B ′ to prevent the influence of reflected light, and noise is increased due to optical loss in the optical isolator. .

  In addition, there is a problem of a band in which the optical isolator performs its function. In other words, there is a limit to the band in which isolation works effectively, so when performing wavelength tuning in a wider wavelength range, if there is reflection from the optical comb in the band where isolation is degraded, interference will occur and noise will increase. Or, the wavelength cannot be changed accurately.

  Therefore, the present invention has been made to solve such problems, and can scan the wavelength of a light source having a narrow band spectrum at a high speed and continuously in a wide band, and further, the required optical isolator. An object of the present invention is to provide a wavelength scanning type laser light source in which the number of the above is reduced and the increase in noise in the optical isolator is reduced.

  Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the description of embodiments described below.

  A wavelength-scanning fiber laser light source according to the present invention includes two Fabry-Perot electro-optic modulators having an electro-optic crystal incorporated in a Fabry-Perot resonator in a space having FSR (Free Spectral Range) close to each other, and an oscillation wavelength. A laser oscillation optical path configured by connecting an optical amplifier having a gain to an optical element for extracting output light with an optical fiber, and at least one of the two Fabry-Perot resonators having the adjacent FSRs A resonator length controller that periodically changes the resonator length of the Perot resonator within a certain range, and is provided by at least one of the two Fabry-Perot electro-optic modulators by the resonator length controller. Light passing therethrough is modulated by a periodic scanning signal.

  A wavelength-scanning fiber laser light source according to the present invention includes a Fabry-Perot electro-optic modulator in which an electro-optic crystal is incorporated in a spatial Fabry-Perot resonator, an optical amplifier having a gain at an oscillation wavelength, and the Fabry-Perot electro-optic modulator. A laser oscillation optical path formed by connecting an optical fiber to a polarization conversion element that rotates the polarization direction of the light emitted from the light and an optical element for extracting output light, and a resonator of the Fabry-Perot electro-optic modulator The Fabry-Perot electro-optic modulator has an FSR (Free Spectral Range) that is close to each of light components of polarization components orthogonal to each other. Functioning as a Fabry-Perot resonator, and by means of the periodic scanning signal given by the resonator length control unit, Characterized by modulating each.

  In the wavelength scanning fiber laser light source according to the present invention, each of the two Fabry-Perot electro-optic modulators is, for example, a ring-type resonance in which a ring-type resonance is obtained by a Fabry-Perot resonator containing an electro-optic crystal. It consists of a Fabry-Perot electro-optic modulator.

  In the wavelength-scanning fiber laser light source according to the present invention, the Fabry-Perot resonator is, for example, a V-type resonant Fabry-Perot electric device that obtains a V-type resonance with a Fabry-Perot resonator containing an electro-optic crystal. It consists of an optical modulator.

  In the wavelength-scanning fiber laser light source according to the present invention, each of the Fabry-Perot electro-optic modulators has a curvature of each concave mirror set so that the Fabry-Perot resonator containing the electro-optic crystal is confocal. Consists of a focal Fabry-Perot electro-optic modulator.

  Furthermore, in the wavelength scanning fiber laser light source according to the present invention, the Fabry-Perot electro-optic modulator includes, for example, two electro-optic crystals arranged so that the C axis is orthogonal between the concave mirrors constituting the Fabry-Perot resonator. It becomes.

  In the present invention, the wavelength of the light source having a narrow band spectrum can be scanned at a high speed and continuously in a wide band, and the number of required optical isolators is reduced, and the increase in noise caused by the optical isolators is reduced. A laser light source of the type can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Needless to say, the present invention is not limited to the following examples, and can be arbitrarily changed without departing from the gist of the present invention.

  A wavelength scanning fiber laser light source 10 according to the present invention is an improvement of the previously proposed wavelength scanning fiber laser light source, and its basic configuration is shown in FIG. Two Fabry-Perot resonators 11A and 11B having a free spectral range), an optical amplifier 12 having a gain at an oscillation wavelength, and an optical coupler connected to the optical amplifier 12 via a polarizer 19 and an isolator 13 via an optical fiber. 14 and at least one of the two Fabry-Perot resonators 11A and 11B, here, a resonator length control unit 15 that periodically changes the resonator length of the Fabry-Perot resonator 11A within a certain range, The optical coupler 14 is connected via an incident side optical system 16A composed of a collimator and a convex lens designed to match the resonance mode of the optical resonator. The Fabry-Perot resonator 11A is connected to a fiber, and one of the Fabry-Perot resonators 11A is designed to match the resonance mode of the optical resonator. Are connected to the other Fabry-Perot resonator 11B via an incident-side optical system 17A composed of a collimator and a convex lens, and the other Fabry-Perot resonator 11B has a collimator function. A fiber ring laser having an optical fiber loop serving as an optical path of laser oscillation connected to the optical amplifier 12 through an optical system 17B as a fiber is configured.

  Here, the polarizer 19 is for determining the polarization state of the light passing through the optical fiber loop, which is an optical path for laser oscillation, and may be inserted at any position in the loop.

  In the wavelength scanning fiber laser light source 10, the two Fabry-Perot resonators 11A and 11B have, for example, a Fabry-Perot resonator containing the electro-optic crystal 110 as a confocal point as shown in FIG. The ring-type resonant Fabry-Perot electro-optic modulator 11 is used in which the curvature of the concave mirrors 111 and 112 is set so as to obtain a ring-type resonance.

  In the ring-type resonant Fabry-Perot electro-optic modulator 11 in which the curvatures of the concave mirrors 111 and 112 are set to be confocal as described above, the direct reflected light Lr with respect to the incident light Lin does not return to the incident side. Do not need.

  Therefore, in this wavelength scanning fiber laser light source 10, the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 in which the direct reflected light Lr with respect to the incident light Lin does not return to the incident side is provided with two units having the FSRs close to each other. By using the Fabry-Perot resonators 11A and 11B, the optical isolators at the input / output portions of the Fabry-Perot resonators 11A and 11B can be omitted, and the isolator 13 is provided only on the input side of the optical amplifier 12.

  That is, in this wavelength scanning fiber laser light source 10, the confocal ring in which the direct reflected light Lr with respect to the incident light Lin does not return to the incident side as the two Fabry-Perot resonators 11A and 11B having the adjacent FSRs as described above. Since the type resonance Fabry-Perot electro-optic modulator 11 is used, the influence of reflection is low. However, in order to determine the clockwise or counterclockwise oscillation direction of the ring laser, only the input side of the optical amplifier 12 is used. An isolator 13 is inserted. This isolator 13 has a purpose different from that for reducing the influence of reflection from a conventional Fabry-Perot electro-optic modulator, and only has a performance that can provide a difference in gain between clockwise and counterclockwise. Not required. Therefore, the problem of the isolator which is a problem in the present invention is solved. Further, the isolator 13 may be inserted at any position in the loop basically.

  In this wavelength scanning fiber laser light source 10, the two Fabry-Perot resonators 11A and 11B having adjacent FSRs function as wavelength selection filters. At least one of the two Fabry-Perot resonators 11A and 11B, here, the Fabry-Perot resonator 11A can vary the selected wavelength by varying the resonator length by the resonator length control unit 15. It can be done.

  The two Fabry-Perot resonators 11A and 11B having the adjacent FSRs can narrow the selection wavelength by the vernier effect by changing the resonator length of one Fabry-Perot resonator 11A. It functions as a bandpass filter having a wavelength selection characteristic of the band.

  In this wavelength scanning fiber laser light source 10, the light that has passed through the band-pass filter by the two Fabry-Perot resonators 11A and 11B having the adjacent FSR provided in the optical fiber loop is amplified by the optical amplifier 12, and the above-mentioned It oscillates by being fed back through the optical fiber loop. In this wavelength scanning fiber laser light source 10, the oscillation wavelength is periodically changed by periodically changing the resonator length of the Fabry-Perot resonator 11A within a certain range by the resonator length control unit 15. The wavelength of the laser light taken out via the optical coupler 14 changes periodically.

  The optical coupler 14 for extracting laser light from the optical fiber loop is provided after the optical amplifier 12, but is provided before the optical amplifier 12 or between the two Fabry-Perot resonators 11A and 11B. May be.

  In the wavelength scanning fiber laser light source 10 having such a configuration, the resonator length of the optical fiber loop can be increased. By setting the resonator length of the optical fiber loop to, for example, 1000 m, the longitudinal mode interval of the entire laser is, for example, 200 kHz. Can be as narrow as possible. As a result, the longitudinal mode interval of the entire laser can be made sufficiently narrower than the bandwidth (FSR / finesse, for example, 2.5 GHz / 50 = 50 MHz) of each of the Fabry-Perot resonators 11A and 11B. The effect of mode hop can be eliminated without changing the resonator length. Therefore, although it is not strictly single mode oscillation, it is possible to tune the wavelength continuously in a pseudo manner simply by changing the selected wavelength of the bandpass filter.

  In this wavelength scanning fiber laser light source 10, the wavelength of a light source having a narrow band spectrum can be continuously scanned at a high speed in a wide band, and the direct reflected light Lr with respect to the incident light Lin does not return to the incident side. Since the above-mentioned two Fabry-Perot resonators 11A and 11B are used as the focus ring-type resonant Fabry-Perot electro-optic modulator 11, the isolator at the input / output portion of each Fabry-Perot resonator 11A and 11B can be omitted. The increase in noise due to optical loss in the optical isolator can be reduced.

  Here, the length of the waveguide-type Fabry-Perot electro-optic modulator can be adjusted by polishing, and the resonator length can be accurately controlled by controlling the temperature of each, so the absolute value of the resonator length is controlled by temperature control. It is possible to control at 1 ppm within the desired range. Therefore, for example, by using a Fabry-Perot electro-optic modulator with FSR = 2.5 GHz and a Fabry-Perot electro-optic modulator with a different FSR by 1/4000, a 10 THz FSR wavelength selection element 4000 times easier due to the vernier effect. realizable. However, in a spatial Fabry-Perot electro-optic modulator that uses a concave mirror, it is difficult to adjust the length with high precision by polishing. Therefore, the position of the concave mirror is adjusted with an accuracy of several microns, and two optical resonators are used. It is necessary to adjust the temperature with high accuracy.

Further, the FSR (Free Spectral Range) of the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 is expressed as follows:
FSR = c / (4 ng · L)
It becomes. Here, c is the speed of light in vacuum, and L is the resonator length.

  In lithium niobate (LN: LiNbO3), which is often used for electro-optic modulation, both the normal light group refractive index nog and the extraordinary light group refractive index neg are both about 2 but there is a difference of 4%. .

Therefore, the FSR of the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 that modulates ordinary light by the electro-optic crystal (LN) 110 is
FSR1 = c / (4 nog · L)
The FSR of the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 that modulates extraordinary light by the electro-optic crystal (LN) 110 is
FSR2 = c / (4 neg · L)
It becomes.

Also, as shown in FIG. 3, a confocal ring-type resonant Fabry-Perot electro-optic modulator 11 includes an electro-optic crystal (LN) 110A having a length L1 and an electro-optic crystal (LN) 110B having a length L2. Then, by arranging the C-axis to be orthogonal, the ordinary light is modulated by the electro-optic crystal (LN) 110A having the length L1, and the extraordinary light is modulated by the electro-optic crystal (LN) 110B having the length L2. The FSR of the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 is
FSR1 = c / (4nog · L1 + 4neg · L2)
A confocal ring-type resonant Fabry-Perot electro-optic modulation in which extraordinary light is modulated by an electro-optic crystal (LN) 110A having a length L1 and ordinary light is modulated by an electro-optic crystal (LN) 110B having a length L2. The FSR of vessel 11 is
FSR2 = c / (4 neg · L1 + 4 nog · L2)
It becomes.

  In this case, if L1 = L2, FSR1 = FSR2, and the difference between FSR1 and FSR2 can be finely set by the difference between the lengths L1 and L2 of the electro-optic crystals (LN) 110A and 110B.

  Here, for the FSR of the ring-type resonant Fabry-Perot electro-optic modulator 11, the calculation formula is shown assuming that the crystal length and the resonator length are the same for the principle explanation, ignoring the space portion.

  Thus, when two crystals are inserted into one Fabry-Perot resonator, the entire resonator length is shared. Originally, what is important for the vernier effect is that the difference between the two FSRs and the ratio between the FSRs is important, so the absolute value of the length is essentially not important, and the difference between the lengths of the two crystals is important. . The difference in length between the two crystals can be adjusted by polishing. Some deviations in the position of the external mirror can be ignored.

  Here, in the wavelength scanning fiber laser light source 10, the resonator length of one Fabry-Perot resonator 11 A of the two Fabry-Perot resonators 11 A and 11 B constituting the bandpass filter is set as a resonator length control unit. 15, the wavelength of the laser light extracted via the optical coupler 14 is periodically scanned by changing the frequency periodically within a certain range. For example, the resonance in the wavelength scanning fiber laser light source 10 shown in FIG. The sawtooth wave signal generated by the sawtooth wave signal generator 150 as a periodic scanning signal is directly supplied to the Fabry-Perot resonator 11B and inverted to the Fabry-Perot resonator 11A as in the device length control unit 15. The configuration is such that it is supplied directly via the amplifier 151, and both the electro-optic modulators in the two Fabry-Perot resonators 11A and 11B are paired. By applying an inverted scanning signal and reciprocally changing the resonator length of each Fabry-Perot resonator, the modulation voltage can be halved, and the voltage is applied to the electro-optic modulator in the Fabry-Perot optical resonator. Since the change in the phase that occurs when adding is canceled out, the wavelength can be scanned more accurately and stably.

  Further, in the wavelength scanning fiber laser light source 10, since the center wavelength is extremely sensitive to the temperature difference between the Fabry-Perot electro-optic modulators, the resonator length control unit 15 in the wavelength scanning fiber laser light source 10 shown in FIG. Then, a part of the laser light extracted through the optical coupler 14, that is, a part of the light passing through the band filter that transmits the center wavelength, is guided from the optical coupler 14 ′ to the photodetector 152 through the band pass filter 16. The detection is performed by the photodetector 152, the phase difference between the timing and the periodic scanning signal is detected by the lock-in amplifier 153, and the control signal is superimposed on the periodic signal so that the phase difference becomes a constant value. The center wavelength is controlled by feedback. As a result, modulation can always be performed at a constant wavelength.

  In addition, as shown in FIG. 3, the L1 electro-optic crystal (LN) 110A and the length L2 electro-optic crystal (LN) 110B are inserted into the confocal ring-type resonant Fabry-Perot electro-optic modulator 11. When the C-axis is arranged so as to be orthogonal to each other, as shown in FIG. 5, the electrodes 130A and 130B of the two electro-optic crystals (LN) 110A and 110B are connected in parallel and modulated by giving a modulation signal. By doing so, the optical distance changes relative to the polarization direction by making the voltages opposite to each other with respect to the C-axis of the crystal.

  Therefore, the change in the optical distance that occurs during one transmission through the crystal is (γ31 · L1) for the polarized light on the FSR1 side when the electro-optic constants γ33, γ31, crystal lengths L1, L2, and crystal thickness d are used. −γ33 · L2) · V / d, and for polarized light on the FSR2 side, (γ33 · L1−γ31 · L2) · V / d, and the difference between them is (γ31−γ33) · (L1 + L2) · The optical distance is modulated by V / d.

  That is, even when two Fabry-Perot electro-optic modulators are used, the inverting amplifier 151 is not necessary if the electrodes can be replaced.

  The crystal selection method is to select a crystal having a large difference between γ33 and γ31. For example, in the case of LN or LT, the stoichiometric composition crystal is more advantageous than the coincidence melt composition crystal.

  Here, a confocal ring-type resonant Fabry-Perot electro-optic modulator 11 in which two electro-optic crystals are inserted into one Fabry-Perot resonator has, for example, a structure as shown in FIG. It is fabricated as a monolithic Fabry-Perot electro-optic modulator.

  First, as shown in FIG. 7A, long crystals 1101, 1102 whose C-axis is perpendicular to the light beam direction and perpendicular to each other, and thin crystals 1201, whose C-axis is in the light beam direction. 1202 is manufactured, each end face orthogonal to the light beam direction is polished, and the length of the electro-optic crystal (LN) 1101 is adjusted to L1, and the length of the electro-optic crystal (LN) 1102 is adjusted to L2.

  Next, as shown in FIG. 7B, the refractive index match between the electro-optic crystal (LN) 1101 of length L1 and the electro-optic crystal (LN) 1102 of length L2 with the C axes orthogonal to each other. Are bonded with an adhesive or an optical contact, and crystals 1201 and 1201 whose thin C-axis is in the light beam direction are bonded to both ends thereof to produce a joined body 1000 having a length of L as a whole. . The crystals 1201 and 1202 in which the thin C-axis at both ends are in the direction of the light beam are isotropic media with respect to the light beam.

  Then, as shown in FIG. 7C, the joined body 1000 is diced to form a base body 1001 of the monolithic Fabry-Perot electro-optic modulator 11.

  Next, as shown in FIG. 7D, the above-mentioned crystals 120A and 120B of the substrate 1001 composed of the electro-optic crystals (LN) 110A and 110B and the crystals 120A and 120B at both ends thus fabricated are shared. The convex surface is polished with a curvature R that becomes a focal point.

Next, as shown in FIG. 7E, confronting confocal concave mirrors 111 and 112 which form Fabry-Perot resonators by coating both end faces of the base body 1001 having the convex surface polished with the curvature R by vapor deposition. Form. Here, the concave mirrors 111 and 112 are formed by coating the end face of the crystal 120A on one side with less than 100% and the end face of the opposite crystal 120B with 100%. The curvature R when the overall length is L is
R = (no / ne-1). (L1 + L2) / 2 + L
It is.

  Then, as shown in FIG. 7F, electrodes are formed by vapor deposition on the side surfaces orthogonal to the C axes of the electro-optic crystals (LN) 110A and 110B of the substrate 1001 where the concave mirrors 111 and 112 are formed on both end surfaces. By forming 130A and 130B, a monolithic Fabry-Perot electro-optic modulator 11 having a structure as shown in FIG. 6 is manufactured.

  In the case of the monolithic Fabry-Perot electro-optic modulator 11, since the crystal size is smaller than that of the collimator, it is difficult to arrange two collimators as the input / output optical systems 16A and 16B. For example, as shown in FIG. In addition, the input / output optical systems 16A and 16B having a prism type mirror 16C on the input surface, or a fiber is mounted on a two-core ferrule as shown in FIG. 9, and a two-core ferrule is formed by the prism 16D. An input / output optical system 16 having a structure in which a fiber mounted on the ring and a ring resonator are coupled to each other is used.

  Here, since the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 can be used as a bidirectional electro-optic modulator, for example, as a wavelength scanning fiber laser light source 10 ′ shown in FIG. As the optical amplifier 12 in the wavelength scanning fiber laser light source 10 shown in FIG. 1, a directional optical amplifier 12 ′ such as SOA that can amplify both polarizations in either direction is used. 14 is provided with a total reflection mirror 14A and a half mirror 14B, and the above-described confocal ring type in which the two Fabry-Perot resonators 11A and 11B having adjacent FSRs function as bidirectional electro-optic modulators, respectively. By configuring the resonant Fabry-Perot electro-optic modulator 11, optical amplification is performed twice during one round of the optical fiber loop. It can be so.

  In this wavelength scanning fiber laser light source 10 ′, light emitted from one Fabry-Perot resonator 11A via the incident / exit optical system 16A ′ is totally reflected by the total reflection mirror 14A, and passes through the incident / exit optical system 16A ′. Is incident on the Fabry-Perot resonator 11A via the incident / exit optical system 16B ′ and enters the other Fabry-Perot resonator 11B via the input / output optical system 17A ′. The incident light that is emitted from the Fabry-Perot resonator 11B through the incident / exit optical system 17B ′ is amplified by the bidirectional optical amplifier 12 ′. Then, light having a predetermined polarization component extracted from the light amplified by the bidirectional optical amplifier 12 ′ via the polarizer 19 is reflected by the half mirror 14 B, and the bidirectional optical amplifier 12 is transmitted via the polarizer 19. The light of a predetermined polarization component that is incident on 'and passes through the polarizer 19 is amplified by the bidirectional optical amplifier 12' and is incident on the Fabry-Perot resonator 11B via the incident / exit optical system 17B '. The light emitted from the Fabry-Perot resonator 11B via the incident / exit optical system is incident on the Fabry-Perot resonator 11A via the incident / exit optical system, and the laser light is extracted through the half mirror 14B.

  In the wavelength-scanning fiber laser light source 10 ′ having such a configuration, the Fabry-Perot resonators 11A and FSR2 of the FSR1 each composed of a confocal ring-type resonant Fabry-Perot electro-optic modulator 11 while the light goes around the fiber loop. The Fabry-Perot resonator 11B is passed twice each, so that the resolution of the optical filter as the vernier effect can be improved, the wavelength selection becomes stronger, the line width is narrow, and the coherent length can be increased. The bidirectional optical amplifier 12 may be inserted at any position in the loop.

  Further, the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 has a different FSR depending on the polarization direction, and the electro-optic modulation is strongly applied to the polarized light in the c-axis direction. Therefore, the wavelength scanning type shown in FIG. Like the fiber laser light source 20, by providing an optical system 18 that separates and combines the polarization components, one confocal ring-type resonant Fabry-Perot electro-optic modulator 11 has two adjacent FSRs. It can function as Fabry-Perot resonators 11A and 11B.

  That is, the wavelength scanning fiber laser light source 20 shown in FIG. 11 is an improvement of the wavelength scanning fiber laser light source 10 shown in FIG. 1, and is a single confocal ring type provided in an optical fiber loop. Resonant Fabry-Perot electro-optic modulator 11, optical amplifier 12 having gain at oscillation wavelength, optical coupler 14 connected to the optical amplifier 12 via an isolator 13, and confocal ring-type resonant Fabry-Perot electro-optic modulation The resonator length controller 15 for periodically changing the relative resonator lengths of the P-polarized light and the S-polarized light in the predetermined range, the optical amplifier 12, the optical coupler 14, the incident side optical system 16A, and the output side optical system 16B. And an optical system 18 for separating and synthesizing the polarization components provided between the two.

  The optical system 18 includes a first PBS coupler 181 to which light emitted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 is incident via an output-side optical system 16B. A first polarization converter 182 to which light of a P-polarized component separated from incident light is incident, and a second polarization converter 183 to which light of an S-polarized component separated from the emitted light by the PBS coupler 181 is incident. The second PBS coupler 184 into which the S-polarized component light is incident via the optical coupler 14.

  In this optical system 18, the first PBS coupler 181 includes light of P-polarized component and light of S-polarized component from the ring-type resonant Fabry-Perot electro-optic modulator 11 that is incident through the output-side optical system 16B. To separate. The P-polarized component light separated from the outgoing light by the first PBS coupler 181 is incident on the first polarization converter 182, and the S-polarized component light is incident on the second polarization converter 183. The

  The first polarization converter 182 rotates the polarization direction of the P-polarized component light separated from the emitted light by the first PBS coupler 181 by 90 ° and converts it into S-polarized component light. The S-polarized component light converted by the first polarization converter 182 is incident on the optical amplifier 12.

  In the wavelength scanning fiber laser light source 20, the S-polarized component light incident via the first polarization converter 182 is amplified by the optical amplifier 12 having a gain at the oscillation wavelength, and the isolator 17 and the optical coupler. 14 and enters the second PBS coupler 184.

  The second polarization converter 183 rotates the polarization direction of the S-polarized light component separated from the emitted light by the first PBS coupler 181 by 90 ° and converts it into P-polarized light. The P-polarized component light converted by the second polarization converter 183 is incident on the second PBS coupler 184.

  Here, the first and second polarization converters 182 and 183 can use a Faraday element, a wave plate, or the like, and also connect the PM fiber to the optical element, and select the PM axis at an appropriate time to change the polarization direction by 90. It can also be set as the structure rotated by a degree.

  The second PBS coupler 184 combines the S-polarized component light incident through the optical coupler 14 and the P-polarized component light incident through the second polarization converter 183.

  Then, the combined light by the second PBS coupler 184 is incident on the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 as incident light through the incident side optical system 16.

  A circulator may be used instead of the first and second PBS couplers 181 and 184.

  In the wavelength scanning fiber laser light source 20, the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 has different FSR depending on the polarization direction, and electro-optic modulation is strongly applied to the polarization in the c-axis direction. , It functions as two Fabry-Perot resonators having different degrees of modulation in the adjacent FSRp and FSRs with respect to incident light, that is, P-polarized component light and S-polarized component light constituting the combined light.

  In this wavelength scanning fiber laser light source 10, one confocal ring-type resonant Fabry-Perot electro-optic modulator 11 that functions as two Fabry-Perot resonators having different degrees of modulation in the adjacent FSRp and FSRs has a wavelength selection function. It functions as a filter, and functions as a bandpass filter having a narrow band wavelength selection characteristic in which the selection wavelength can be varied by the vernier effect by varying the relative resonator length of P-polarized light and S-polarized light.

  The wavelength scanning fiber laser light source 20 passed through a bandpass filter formed by one confocal ring-type resonant Fabry-Perot electro-optic modulator 11 having the above-mentioned close FSRp and FSRs provided in an optical fiber loop. The light, that is, the light emitted from the ring-type resonant Fabry-Perot electro-optic modulator 11 is separated into P-polarized component light and S-polarized component light by the first PBS coupler 181, and the first PBS coupler 181 The P-polarized component light separated from the emitted light is converted into S-polarized component light by the first polarization converter 182, amplified by the optical amplifier 12, fed back through the optical fiber loop, and the first The S polarization component light separated from the emitted light by the one PBS coupler 181 is sent to the second polarization converter 183. Ri is converted into P-polarized light component that oscillates by being fed back. In this wavelength scanning fiber laser light source 10, the relative length of the P-polarized light and the S-polarized light of the single confocal ring-type resonant Fabry-Perot electro-optic modulator 11 is made constant by the resonator length controller 15. By periodically changing in the range, the oscillation wavelength periodically changes, and the wavelength of the laser light extracted via the optical coupler 14 changes periodically.

  This wavelength scanning fiber laser light source 20 uses a single confocal ring-type resonant Fabry-Perot electro-optic modulator 11 in which direct reflected light Lr with respect to incident light Lin does not return to the incident side. The wavelength of a light source having a narrow band spectrum that generates optical light can be continuously scanned at a high speed in a wide band.

Here, as described above, in the case of two Fabry-Perot resonators, FSR1 = c / (4 ng · L1)
FSR2 = c / (4 ng · L2)
Therefore, approximately (FSR1-FSR2) / FSR = (L2-L1) / L
For example, if a difference of 1/1000 is to be made, the difference between L1 and L2 is set to a difference of 1/1000. Therefore, the length is adjusted with an accuracy of 1/1000 or less of L by polishing, and the temperature difference In the case of one Fabry-Perot resonator, FSR1 = c / (4nog · L1 + 4neg · L2)
FSR2 = c / (4 neg · L1 + 4 nog · L2)
Therefore, approximately (FSR1-FSR2) / FSR = (L2-L1) / L (nog-neg) / ng
Since (nog−neg) / ng is about 0.04, even if the polishing accuracy is the same, the difference in length may be set to 1/40 of L. Since the polishing accuracy is about 1/1000, the FSR difference can be realized with an accuracy of 1/1000 ± 1/40000 or less by polishing alone. At this time, it is possible to thermally couple the two crystals because they are close to each other, and the accuracy of the difference in FSR obtained by polishing can be maintained without temperature control. There is no need for temperature control to make the FSR difference constant as used in the waveguide type. Therefore, there is no need for two temperature controllers, and there is a cost merit.

  Further, as described above, the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 can be used as a bi-directional electro-optic modulator, and thus, for example, a wavelength scanning fiber laser light source 20 ′ shown in FIG. Further, as the optical amplifier 12 in the wavelength scanning fiber laser light source 20 shown in FIG. 11, a bidirectional optical amplifier 12 ′ such as SOA that can amplify both polarizations in either direction is used. A total reflection mirror 14A and a half mirror 14B are provided in place of the optical coupler 14, and one confocal ring-type resonant Fabry-Perot functioning as two Fabry-Perot resonators having different modulation degrees in the above-mentioned adjacent FSRp and FSRs. The electro-optic modulator 11 may be configured to be used in both directions.

  In this wavelength scanning fiber laser light source 20 ′, all the light extracted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 through the incident / exit optical system 16 A ′ passes through the second PBS coupler 184. The light incident on the reflection mirror 14A and reflected by the total reflection mirror 14A passes through the second PBS coupler 184 and passes through the incident / exit side optical system 16A ′, so that the confocal ring-type resonant Fabry-Perot electricity Light that is incident on the optical modulator 11 and is extracted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 via the input / output optical system 16B ′ is the first PBS coupler 181 and the first and polarized light. The light that passes through the converter 182 and enters the bidirectional optical amplifier 12 ′ and is amplified by the bidirectional optical amplifier 12 ′ is half mirror 14B. The light incident and reflected by the half mirror 14B is incident on the bidirectional optical amplifier 12 ′, and the light amplified by the bidirectional optical amplifier 12 ′ is the first and polarization converters 182 and the first PBS. The laser beam is oscillated by being incident on the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 from the incident / exit side optical system 16B ′ via the coupler 181 and the laser light is extracted via the half mirror 14B.

  In the wavelength-scanning fiber laser beam 210 ′ having such a configuration, one confocal ring-type resonant Fabry-Perot electro-optic that functions as two Fabry-Perot resonators having different modulation degrees in the above-mentioned adjacent FSRp and FSRs. By using the modulator 11 in both directions, the FSR1 Fabry-Perot resonator and the FSR2 Fabry-Perot resonator comprising the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 while the light goes around the fiber loop. 2 is passed twice, so that the resolution of the optical filter as the vernier effect can be improved, the wavelength selection becomes stronger, the line width is narrow, and the coherent length can be increased. The bidirectional optical amplifier 12 may be inserted at any position in the loop. For example, if the bidirectional optical amplifier 12 is inserted before or after the second polarization converter 183, the light goes around the fiber loop, that is, is shared. Since it can be amplified twice while passing through the Fabry-Perot resonator of FSR1 and the Fabry-Perot resonator of FSR2 composed of the ring-type resonant Fabry-Perot electro-optic modulator 11 at the focal point, it is advantageous for SN.

  Further, since the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 can be used as a bidirectional electro-optic modulator, the proximity scanning fiber laser light source 30 shown in FIG. The light is incident / exited to / from one confocal ring-type resonant Fabry-Perot electro-optic modulator 11 having the FSRp and FSRs via the incident / exit side optical system 16A ′ and the incident / exit side optical system 36B. The light emitted through the entrance / exit side optical system 16A ′ enters the entrance / exit side optical system 16A ′ via the first optical fiber loop 31 and exits through the entrance / exit side optical system 16B ′. The light may be incident on the incident / exit optical system 16B ′ via the second optical fiber loop 32.

  In the wavelength scanning fiber laser light source 30, the light emitted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 through the incident / exit side optical system 16 A ′ is P-polarized by the first PBS coupler 311. The P-polarized component light is separated into component light and S-polarized component light, and the polarization direction is rotated by 90 ° by the first polarization converter 312 and converted into S-polarized component light. The first optical fiber loop 31 is configured such that the light of the S-polarized component incident and amplified by the optical amplifier 12 is returned to the first PBS coupler 311 via the isolator 13 and the optical coupler 14. From the first PBS coupler 311 to the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 via the input / output side optical system 16A ′. It is. In addition, the light emitted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 through the incident / exit side optical system 16B ′ is reflected by the second PBS coupler 321 into P-polarized component light and S-polarized component light. The P-polarized component light and the S-polarized component light separated into light are rotated by 90 ° by the second polarization converter 322 and synthesized by the second PBS coupler 321. Two optical fiber loops 32 are configured, and the combined light from the second PBS coupler 321 is incident on the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 via the incident / exit-side optical system 16B ′. The

  That is, in the wavelength scanning fiber laser light source 30, the light emitted through the incident / exit side optical system 16 A ′ of the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 is converted into the first optical fiber loop 31. And is incident on the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 via the incident / exit-side optical system 16A ′, and the confocal ring-type resonant Fabry-Perot electro-optic modulator. The light emitted from 11 through the incident / exit side optical system 16B ′ is rotated by 90 ° in the polarization direction in the second optical fiber loop, and the confocal ring-type resonance is performed through the incident / exit side optical system 16B ′. An optical fiber loop is configured to be incident on the Fabry-Perot electro-optic modulator 11.

  In this wavelength scanning fiber laser light source 30, a single confocal ring-type resonant Fabry-Perot electro-optic modulator 11 in which direct reflected light Lr with respect to incident light Lin does not return to the incident side is used as a bidirectional electro-optic modulator. By using this, it is possible to continuously scan the wavelength of a light source having a narrow band spectrum that generates monochromatic light with extremely low noise in a wide band at high speed.

  The polarization direction of the light emitted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 via the incident / exit side optical system 16B ′ is rotated by 90 ° and the incident / exit side optical system 16B ′. In place of the first optical fiber loop returned to the confocal ring-type resonant Fabry-Perot electro-optic modulator 11, a Faraday rotator 323 and a total reflection mirror are used as in a wavelength scanning fiber laser light source 30 'shown in FIG. 324 can also be used.

  This wavelength scanning fiber laser light source 30 ′ is an improvement on the wavelength scanning fiber laser light source 30 shown in FIG. 13 except that the second optical fiber loop 32 is replaced with a Faraday rotator 323 and a total reflection mirror 324. Is the same as that of the wavelength scanning fiber laser light source 30 described above, and the same components are denoted by the same reference numerals and detailed description thereof is omitted.

  In this wavelength scanning fiber laser light source 30 ′, the light emitted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 through the incident / exit side optical system 16 B ′ has a polarization direction of 45 ° by the Faraday rotator 323. The light rotated and incident on the total reflection mirror 324 is totally reflected by the total reflection mirror 324, and the polarization direction is further rotated by 45 ° by the Faraday rotator 323 so that the confocal light is incident from the incident / exit side optical system 16B ′. The light is incident on the ring-type resonant Fabry-Perot electro-optic modulator 11.

  Also in this wavelength scanning fiber laser light source 30 ′, one confocal ring-type resonant Fabry-Perot electro-optic modulator 11 in which the direct reflected light Lr with respect to the incident light Lin does not return to the incident side is bidirectionally modulated. It can be used as a scanner and can continuously scan the wavelength of a light source having a narrow band spectrum that generates monochromatic light with extremely low noise in a wide band at high speed.

  Further, for example, an optical amplifier such as an SOA can amplify both polarizations in either direction. For example, as in the wavelength scanning fiber laser light source 40 shown in FIG. By providing the optical amplifier 31, optical amplification can be performed twice during one round of the optical fiber loop.

  The wavelength scanning fiber laser light source 40 shown in FIG. 15 is an improved version of the wavelength scanning fiber laser light source 30 ′ shown in FIG. 14, and the first optical fiber loop 31 is replaced with a bidirectional optical amplifier 41 and a Faraday rotator. Since it is the same as that of the wavelength scanning fiber laser light source 30 ′ except that it is replaced with 42 and the half mirror 43, the same components are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this wavelength scanning fiber laser light source 40, the light emitted from the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 via the incident / exit side optical system 16A ′ is amplified by the bidirectional optical amplifier 41, and the Faraday When the polarization direction is rotated by 45 ° by the rotator 42, it enters the half mirror 43, and the light reflected by the half mirror 43 is further rotated by 45 ° by the Faraday rotator 42 and enters the bidirectional optical amplifier 41. The light amplified by the bidirectional optical amplifier 41 oscillates by being incident on the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 from the incident / exit optical system 16A ′, and the half mirror 43 is caused to oscillate. The laser beam is taken out through.

  Further, in the confocal resonant Fabry-Perot electro-optic modulator, V-shaped resonance can be obtained by adjusting the incident direction of incident light. For example, the confocal V-shaped resonant Fabry-Perot electro-optic modulation shown in FIG. The curvature of each concave mirror 511, 512 is set so that the Fabry-Perot resonator containing the electro-optic crystal 510 is confocal, as in the case 51, and the incident light Lin is adjusted to adjust the incident direction of the incident light Lin. V-shaped resonance in which the outgoing light Lout returns in the incident direction without the direct reflected light Lr of Lin returning in the incident direction can be obtained.

  Therefore, a confocal V-type resonant Fabry-Perot electro-optic modulator 51 that can obtain a V-shaped resonance in which outgoing light returns in the incident direction without direct reflection of incident light returning in the incident direction is used. Thus, for example, a linear resonance type wavelength scanning fiber laser light source 50 as shown in FIG. 17 can be configured.

  This wavelength scanning fiber laser light source 50 includes two confocal V-type resonant Fabry-Perot electro-optic modulators 51A and 51B, and one V-type resonant Fabry-Perot electro-optic modulator 51A with an input / output side optical system 52A. A bi-directional optical amplifier 53 connected through an optical fiber, an optical coupler 54 connected to the other V-type resonant Fabry-Perot electro-optic modulator 51B through an optical system 52B, and the above two units. One of the V-type resonant Fabry-Perot electro-optic modulators 51A and 51B, here, a resonator length control unit 55 that periodically changes the resonator length of the V-type resonant Fabry-Perot electro-optic modulator 51A within a certain range. The bidirectional optical amplifier 53 and the optical coupler 54 are optically connected.

  The two confocal V-shaped resonant Fabry-Perot electro-optic modulators 51A and 51B have FSRs (Free spectral ranges) close to each other, and each function as a wavelength selection filter. Then, at least one of the two confocal V-shaped Fabry-Perot resonators 51A and 51B, here, the Fabry-Perot resonator 51A can change the selected wavelength by changing the resonator length. It has become.

  The two V-type resonant Fabry-Perot electro-optic modulators 51A and 51B having the FSRs close to each other can change their vernier effect by changing the resonator length of one V-type resonant Fabry-Perot electro-optic modulator 51A. Therefore, it functions as a band pass filter having a narrow band wavelength selection characteristic that can change the selection wavelength.

  In this wavelength scanning fiber laser light source 50, the light passing through the band-pass filter by the two V-type Fabry-Perot resonators 51A and 51B having the adjacent FSRs is between the V-type Fabry-Perot resonators 51A and 51B. Oscillates by being amplified by the bidirectional optical amplifier 53 having a gain in the oscillation wavelength when reciprocating through. In this wavelength scanning fiber laser light source 50, the oscillation wavelength is periodically changed by periodically changing the resonator length of the V-type Fabry-Perot resonator 51A by a resonator length control unit 55 within a certain range. In addition, the wavelength of the laser light extracted through the optical coupler 54 is changed periodically.

  In the wavelength scanning fiber laser light source 50 having such a configuration, the resonance length can be increased by increasing the length of the optical path connected to the optical fiber, thereby reducing the longitudinal mode interval of the entire laser and reducing the resonance length. The effect of mode hopping can be eliminated without changing, and strictly speaking, it is not single mode oscillation, but by changing the selected wavelength of the bandpass filter, the wavelength can be tuned continuously in a pseudo manner. Can do.

  In this wavelength scanning fiber laser light source 50, the wavelength of a light source having a narrow band spectrum can be continuously scanned at a high speed in a wide band, and the direct reflected light Lr with respect to the incident light Lin does not return to the incident side. Since the focal V-type resonant Fabry-Perot electro-optic modulator 51 is used for the Fabry-Perot resonators 51A and 51B, the isolator can be omitted, and the increase in noise due to optical loss in the optical isolator can be reduced.

  Similarly to the confocal ring-type resonant Fabry-Perot electro-optic modulator 51, the confocal V-type resonant Fabry-Perot electro-optic modulator 51 includes two electro-optic crystals so that the C-axis is orthogonal between the concave mirrors. By arranging, the difference in FSR can be set finely by the difference in length.

  Further, the confocal V-type resonant Fabry-Perot electro-optic modulator 51 has different FSR depending on the polarization direction, and the electro-optic modulation is strongly applied to the polarized light in the c-axis direction. For example, as shown in FIG. In addition, a linear resonance type wavelength scanning fiber laser light source 60 can be configured by one confocal V-type resonance Fabry-Perot electro-optic modulator 51.

  This wavelength-scanning fiber laser light source 60 is an improvement of the wavelength-scanning fiber laser light source 50 shown in FIG. 17, and includes one confocal V-type resonant Fabry-Perot electro-optic modulator 51 and the V-type resonance. A bidirectional optical amplifier 53 optically connected to the Fabry-Perot electro-optic modulator 51 via an input / output optical system 52, a Faraday rotator 64 optically connected to the bidirectional optical amplifier 53, and the Faraday rotator 64 A half mirror 65 connected to the optical fiber is provided.

  In this wavelength scanning fiber laser light source 60, the light emitted from the confocal V-type resonant Fabry-Perot electro-optic modulator 51 through the incident / exit side optical system 52 is amplified by the bidirectional optical amplifier 53, and is Faraday rotator. When the polarization direction is rotated by 45 ° by 64, the light is incident on the half mirror 65, and the light reflected by the half mirror 65 is further rotated by 45 ° by the Faraday rotator 65 and incident on the bidirectional optical amplifier 53. The light amplified by the bidirectional optical amplifier 53 enters the confocal V-type resonant Fabry-Perot electro-optic modulator 51 from the incident / exit side optical system 52.

  In this wavelength scanning fiber laser light source 50, the confocal V-type resonant Fabry-Perot electro-optic modulator 51 has different FSR depending on the polarization direction, and electro-optic modulation is strongly applied to the polarization in the c-axis direction. , It functions as two Fabry-Perot resonators having different degrees of modulation in the adjacent FSRp and FSRs with respect to incident light, that is, P-polarized component light and S-polarized component light constituting the combined light.

  The one confocal V-type resonant Fabry-Perot electro-optic modulator 51 that functions as two Fabry-Perot resonators having different modulation degrees in the adjacent FSRp and FSRs functions as a wavelength selection filter, and includes P-polarized light and S-polarized light. By varying the relative resonator length of the polarized light, it functions as a bandpass filter having a narrow band wavelength selection characteristic that can vary the selected wavelength by its vernier effect.

  In the wavelength scanning fiber laser light source 60, the light emitted from the confocal V-type resonant Fabry-Perot electro-optic modulator 51 is reflected by the half mirror 65 and the confocal V-type resonant Fabry-Perot electro-optic modulator. It returns to 51 and oscillates by being amplified by the bidirectional optical amplifier 53 having a gain at the oscillation wavelength. In the wavelength scanning fiber laser light source 60, the relative resonator lengths of the P-polarized light and the S-polarized light of the V-type resonant Fabry-Perot electro-optic modulator 51 are periodically changed within a certain range by the resonator length control unit 55. By doing so, the oscillation wavelength changes periodically, and the wavelength of the laser beam extracted through the half mirror changes periodically.

  In the wavelength scanning fiber laser light source 60 having such a configuration, the resonance length can be increased by increasing the length of the optical path connected to the optical fiber, thereby reducing the longitudinal mode interval of the entire laser and reducing the resonance length. The effect of mode hopping can be eliminated without changing, and strictly speaking, it is not single mode oscillation, but by changing the selected wavelength of the bandpass filter, the wavelength can be tuned continuously in a pseudo manner. Can do.

  Therefore, this wavelength scanning fiber laser light source 60 uses a single confocal V-type resonant Fabry-Perot electro-optic modulator 51 in which the direct reflected light Lr with respect to the incident light Lin does not return to the incident side. The wavelength of a light source having a narrow band spectrum that generates small monochromatic light can be continuously scanned at a high speed in a wide band.

  Here, in the embodiment of the invention described above, the confocal ring-type resonant Fabry-Perot electro-optic modulator 11 (11A, 11B) or the confocal V-type resonant Fabry-Perot electro-optic modulator 51 (51A, 51A, 51B). 51B), the wavelength-scanning laser light source configured by using the ring-type resonant Fabry-Perot electro-optic modulator 11 (11A, 11B) and the V-type resonant Fabry-Perot electro-optic modulator 51 (51A, 51B) In principle, the light beam may not be confocal as long as light can be coupled to the single transverse mode.

  That is, a spatial Fabry-Perot electro-optic modulator can also be used as the ring-type resonant Fabry-Perot electro-optic modulator 11 (11A, 11B) or the V-type resonant Fabry-Perot electro-optic modulator 51 (51A, 51B).

  Using a spatial Fabry-Perot electro-optic modulator has the advantage of reducing loss and increasing finesse. In the optical path, the loss is about 7 dB per unit and the finesse is about 50, but the loss is about 1 dB and the finesse is about 400 in the spatial type. In this case, the SN ratio is improved by reducing the loss, and the finesse improvement increases the resolution as a wavelength filter, so that the coherent length of the wavelength tunable laser can be increased.

  Further, by making the Fabry-Perot electro-optic modulator in the space “ring-type” or “V-shaped”, direct reflection can be prevented, thereby reducing the number of isolators.

  A "ring-type" or "V-shaped" Fabry-Perot electro-optic modulator is theoretically not confocal as long as it can couple light into a single transverse mode. If the light cannot be coupled into a single transverse mode with slight adjustments, the unwanted transverse mode will appear and will be different from the desired mode frequency, thus disturbing the vernier effect. In a confocal "ring-type" or "V-shaped" Fabry-Perot electro-optic modulator, the resonance frequency of the transverse mode is degenerated, so even if there is a lack of adjustment, use it without causing unnecessary modes. Can do.

  Here, a measurement system 200 as shown in FIG. 19 is constructed, and the wavelength of the laser beam output from the wavelength scanning light source 10 due to the vernier effect is measured by the interferometer 210 to constitute the bandpass filter. FIG. 6 shows the result of obtaining the relationship between the scanning signal voltage provided by the resonator length control unit 15 that changes the resonator length of one Fabry-Perot resonator 11A of the two Fabry-Perot resonators 11A and 11B and the laser frequency. FIG. 20B shows the result of plotting the deviation of the measured value from the linear approximation value. 20A and 20B, the horizontal axis represents the scanning signal voltage, and the vertical axis in FIG. 20A represents the laser frequency corresponding to the wavelength obtained as a measurement result. The vertical axis of B) is the amount of deviation of the laser frequency measurement value from the linear approximation value.

  Further, when the waveform of the scanning signal given to the Fabry-Perot resonator 11A by the resonator length control unit 15 and the waveform of the interference signal obtained by the interferometer 210 are observed, (A), (B), ( As shown in C), an interference signal waveform following the scanning signal waveform (triangular wave, sine wave, sawtooth wave) was obtained.

  Here, in the measurement system 200 shown in FIG. 19, an SOA (semiconductor optical amplifier) is used as the optical amplifier 12 of the wavelength scanning fiber laser light source 10, and a 1 km SM fiber and a Faraday mirror are used as the delay line 18. A delay line using a PBS coupler was inserted. Further, the synchronized function generator 2 channels are used as the resonator length control unit 15 so that the Fabry-Perot resonators 11A and 11B can be modulated with arbitrary waveforms.

  In the measurement system 200, the wavelength tunable range is increased by using the SOA for the optical amplifier 12. 20A shows the result of measuring the change in the frequency (wavelength) of the laser by applying a voltage to the bias of one Fabry-Perot resonator 11A. Looking at the data, the variable wavelength reaches 10 THz. You can see that 10 THz is approximately 80 nm, which is larger than the experimental data 33 nm of FIG. 30 obtained by the system of FIG. Here, as a temperature condition, the temperature difference between the two Fabry-Perot resonators 11A and 11B is set to 8 degrees.

  Further, in this measurement system 200, modulation is possible at an integral multiple of 100 kHz by inserting a delay line 18 into the wavelength scanning fiber laser light source 10. In the case of a delay line using a 1 km SM fiber, a Faraday mirror, and a PBS coupler, light travels back and forth through the fiber, which is equivalent to a 2 km delay line. The data in FIG. 21 is data at a scanning frequency of 200 kHz, and the temperature condition is the same 8 degrees. The scanning range is 10 THz.

  Further, at this time, by using a synchronized two-channel function generator as the resonator length control unit 15 and applying an inverted scanning signal to each of the Fabry-Perot resonators 11A and 11B, the wavelength change direction is affected. Good modulation was obtained as shown in FIG. When a scanning signal exceeding 100 kHz was applied to only one Fabry-Perot resonator 11A, the light intensity varied depending on the direction of change in wavelength, or problems such as laser oscillation stopped. By adding an inverted scanning signal to 11A and 11B, the degree of these problems was greatly reduced. Thereby, the scanning frequency could be confirmed up to at least 1 MHz.

  When an inverted scanning signal is applied to each Fabry-Perot resonator 11A, 11B, the distance between the two Fabry-Perot resonators 11A, 11B cannot be ignored, particularly at a high scanning frequency (about 1 MHz). It is necessary to adjust the phase difference between the inverted scanning signals applied to the respective Fabry-Perot resonators 11A and 11B.

  As is apparent from the above measurement results, the laser frequency in the wavelength scanning light source 10 due to the vernier effect is substantially proportional to the scanning signal voltage by the resonator length control unit 15.

  That is, in the wavelength scanning light source 10 by the vernier effect, the wavelength of the light is proportional to the input voltage signal. Therefore, for example, if the input electric signal is modulated by a linear sawtooth wave or the like, the sawtooth wavelength can be modulated. In particular, since the wavelength can be controlled by an electrical EO effect, there is no hysteresis caused by mechanical modulation.

  Further, the wavelength scanning light source 10 based on the vernier effect is capable of modulation in a sawtooth waveform such that the wave number is equally spaced in time by adjusting an electrical signal to a non-linear sawtooth wave.

That is, when α is a constant, the wavelength with respect to the voltage V is
λ = α · V + λ ₀
It is. On the other hand, the wave number K of light is
K = 2π / λ = 2π / (α · V + λ ₀ )
Therefore, in order to realize the wave number which is the function K (t) for an arbitrary time, the function V (t) for the voltage time is expressed as V (t) = (2π / K (t) −λ ₀ ) / α
And it is sufficient.

  Therefore, in the wavelength scanning fiber laser light source 10, the resonator length control unit sets the resonator length of at least one Fabry-Perot resonator 11A out of the two Fabry-Perot resonators 11A and 11B constituting the bandpass filter. In order to periodically scan the wavelength of the laser light extracted via the optical coupler 14 by periodically changing the frequency of the laser beam 15 through the optical coupler 14, the resonator length control unit 15 is previously connected to the Fabry-Perot resonator 11A. By adjusting the waveform of the scanning signal to be applied and calibrating so that the wave number of the laser light extracted via the optical coupler 14 is linear with respect to time, the laser light having a wave number linear with respect to time is converted into the optical coupler 14. Can be obtained through.

  For example, like the wavelength scanning fiber laser light source 10 shown in FIG. 22, the resonator length control unit 15 reads calibration data for obtaining laser light whose wave number is linear with respect to time from the ROM 15A, and generates the waveform of the scanning signal. By using the configuration for generation, laser light whose wave number is linear with respect to time can be obtained via the optical coupler 14.

  Also, in each of the wavelength scanning fiber laser light sources 10 ′, 20, 20 ′, 30, 30 ′, 40, 50, 60, the waveform of the scanning signal is adjusted, and the wave number of the laser light extracted through the optical element is adjusted. By calibrating so as to be linear with respect to time, a laser beam whose wave number is linear with respect to time can be obtained.

1 is a block diagram showing a basic configuration of a wavelength scanning laser light source including two confocal Fabry-Perot electro-optic modulators according to the present invention. FIG. It is sectional drawing which shows typically the structure of the confocal ring-type resonant Fabry-Perot electro-optic modulator used for the said wavelength scanning laser light source. It is sectional drawing which shows typically the structure of the confocal Fabry-Perot electro-optic modulator formed by arrange | positioning two electro-optic crystals so that C-axis may be orthogonally crossed between concave mirrors. It is a block diagram which shows the structural example of the resonator length control part made to control the center wavelength of the band pass filter comprised by two Fabry-Perot resonators. It is a figure which shows typically the connection structure for supplying the modulation | alteration signal of the confocal Fabry-Perot electro-optic modulator formed by arrange | positioning two electro-optic crystals so that C axis may be orthogonally crossed between concave mirrors. It is a figure which shows typically the manufacture example of a monolithic type Fabry-Perot electro-optic modulator. It is a figure which shows typically the manufacture process of the said monolithic type Fabry-Perot electro-optic modulator. It is a figure which shows typically the manufacture example of a monolithic type Fabry-Perot electro-optic modulator. FIG. 2 is a diagram schematically illustrating a monolithic Fabry-Perot electro-optic modulator including an input / output optical system having a structure in which a prism type mirror is provided on an input surface. It is a figure which shows typically the monolithic type Fabry-Perot electro-optic modulator provided with the incident / exit optical system of the structure which couple | bonds the fiber mounted in the two-core ferrule with a prism, and a ring type resonator. It is a block diagram which shows the other structural example of the wavelength scanning laser light source provided with two confocal Fabry-Perot electro-optic modulators concerning this invention. 1 is a block diagram showing a basic configuration of a wavelength scanning laser light source including one confocal Fabry-Perot electro-optic modulator according to the present invention. FIG. It is a block diagram which shows the other structural example of the wavelength scanning laser light source provided with one confocal Fabry-Perot electro-optic modulator which concerns on this invention. It is a block diagram which shows the other structural example of the wavelength scanning laser light source provided with one confocal Fabry-Perot electro-optic modulator which concerns on this invention. It is a block diagram which shows the other structural example of the wavelength scanning laser light source provided with one confocal Fabry-Perot electro-optic modulator which concerns on this invention. It is a block diagram which shows the other structural example of the wavelength scanning laser light source provided with one confocal Fabry-Perot electro-optic modulator which concerns on this invention. It is sectional drawing which shows typically the structure of the confocal V-shaped resonant Fabry-Perot electro-optic modulator used for the wavelength scanning laser light source which concerns on this invention. 1 is a block diagram showing a configuration of a linear resonance type wavelength scanning fiber laser light source configured by using two confocal V-type resonant Fabry-Perot electro-optic modulators according to the present invention. FIG. 1 is a block diagram showing a configuration of a linear resonance type wavelength scanning fiber laser light source configured by using one confocal V-type resonant Fabry-Perot electro-optic modulator according to the present invention. FIG. It is a figure which shows the result of having measured the relationship between the scanning signal voltage and laser frequency in the wavelength scanning laser light source which concerns on this invention. It is a block diagram which shows the structure of the measurement system for measuring the relationship between the said scanning signal voltage and a laser frequency. It is a figure which shows the observation result of the waveform of the scanning signal which the said resonator length control part gives to a Fabry-Perot resonator, and the waveform of the interference signal obtained with an interferometer. It is a block diagram which shows the structural example of the wavelength scanning fiber laser light source which can obtain a laser beam with a wave number linear with respect to time via an optical coupler. It is a block diagram which shows the fundamental structure of the wavelength variable light source proposed conventionally. It is a block diagram which shows the basic composition of the wavelength scanning laser light source proposed previously. It is a figure which shows the transmission spectrum of a normal optical resonator. It is a figure which shows the transmission spectrum at the time of connecting two optical resonators in which FSR differs 1% in cascade. It is the figure which expanded and showed a part of transmission spectrum shown in FIG. It is a block diagram which shows the actual structural example of the wavelength scanning laser light source which used the Fabry-Perot electro-optic modulator for the said 2 Fabry-Perot resonators. It is a block diagram which shows the structure of the fiber ring laser which uses the optical fiber amplifier for wavelength 1.5 micrometer band, two comb generator modules, and an optical coupler. It is a figure which shows the measurement result of the said fiber ring laser.

Explanation of symbols

10, 10 ', 20, 20', 30, 30 ', 40, 50, 60 Wavelength scanning fiber laser light source 11, 11A, 11B Ring-type resonant Fabry-Perot electro-optic modulator 12 Optical amplifier 12' Bidirectional optical amplifier 13 Isolators 14, 14 ', 54 Optical coupler 14A Total reflection mirror 14B Half mirror 15 Resonator length controller 15A ROM
16A, 17A Incident-side optical systems 16B, 17B Emission-side optical systems 16A ′, 16B ′, 52, 52A, 52B, Incoming / outgoing-side optical system 18 Optical systems 31, 32 for separating and combining polarization components Optical fiber loops 41, 53 Bidirectional optical amplifiers 42, 64, 323 Faraday rotator 43, 65 Half mirror 51, 51A, 51B V-type resonant Fabry-Perot electro-optic modulator 110, 110A, 110B, 510 Electro-optic crystal 111, 112, 511, 512, concave mirror 181 , 184, 311, 321 PBS couplers 182, 183, 312, 322 Polarization conversion element 324 Total reflection mirror

Claims (11)

Two Fabry-Perot electro-optic modulators in which an electro-optic crystal is incorporated in a Fabry-Perot resonator in a space having an FSR (Free Spectral Range) close to each other, an optical amplifier having a gain at an oscillation wavelength, and output light are extracted. An optical path of laser oscillation configured by connecting an optical element with an optical fiber;
A resonator length controller that periodically changes the resonator length of at least one Fabry-Perot resonator of the two Fabry-Perot resonators having the adjacent FSRs in a certain range;
A wavelength-scanning fiber laser light source, wherein light passing therethrough is modulated by a periodic scanning signal provided by the resonator length control unit at least one of the two Fabry-Perot electro-optic modulators.   Each of the two Fabry-Perot electro-optic modulators includes a ring-type resonant Fabry-Perot electro-optic modulator configured to obtain a ring-type resonance with a Fabry-Perot resonator including an electro-optic crystal. Item 6. A wavelength scanning fiber laser light source according to Item 1.   2. The two Fabry-Perot resonators each comprising a V-type resonant Fabry-Perot electro-optic modulator configured to obtain a V-type resonance with a Fabry-Perot resonator containing an electro-optic crystal. The wavelength scanning fiber laser light source described.   Each of the two Fabry-Perot electro-optic modulators comprises a confocal Fabry-Perot electro-optic modulator in which the curvature of each concave mirror is set so that the Fabry-Perot resonator containing the electro-optic crystal is confocal. The wavelength-scanning fiber laser light source according to claim 2 or 3,   2. The wavelength scanning fiber according to claim 1, wherein the Fabry-Perot electro-optic modulator is formed by arranging two electro-optic crystals between the concave mirrors constituting the Fabry-Perot resonator so that the C-axis is orthogonal. Laser light source. A Fabry-Perot electro-optic modulator in which an electro-optic crystal is housed in a spatial Fabry-Perot resonator, an optical amplifier having a gain at an oscillation wavelength, and a polarization direction of light emitted from the Fabry-Perot electro-optic modulator rotated by 90 ° A laser oscillation optical path configured by connecting an optical fiber to a polarization conversion element to be output and an optical element for extracting output light;
A resonator length controller for periodically changing the resonator length of the Fabry-Perot electro-optic modulator in a certain range;
The Fabry-Perot electro-optic modulator functions as two Fabry-Perot resonators having FSRs (Free Spectral Ranges) close to each of the polarized light components orthogonal to each other, and is provided by the resonator length control unit. A wavelength-scanning fiber laser light source characterized by modulating each of polarized light components orthogonal to each other by a periodic scanning signal.   7. The Fabry-Perot electro-optic modulator comprising a ring-type resonant Fabry-Perot electro-optic modulator configured to obtain a ring-type resonance with a Fabry-Perot resonator including the electro-optic crystal. Wavelength scanning fiber laser light source.   7. The wavelength scanning according to claim 6, wherein the Fabry-Perot resonator comprises a V-type resonant Fabry-Perot electro-optic modulator configured to obtain a V-type resonance with the Fabry-Perot resonator including the electro-optic crystal. Type fiber laser light source.   The Fabry-Perot electro-optic modulator comprises a confocal Fabry-Perot electro-optic modulator in which the curvature of each concave mirror is set so that a Fabry-Perot resonator containing an electro-optic crystal is confocal. Item 9. The wavelength scanning fiber laser light source according to Item 7 or Item 8.   7. The wavelength scanning fiber according to claim 6, wherein the Fabry-Perot electro-optic modulator is formed by arranging two electro-optic crystals so that the C axis is orthogonal between concave mirrors constituting the Fabry-Perot resonator. Laser light source.   By adjusting the waveform of the periodic scanning signal given to the Fabry-Perot resonator by the resonator length control unit, the wave number of the laser light extracted through the optical element is made linear with respect to time. 7. The wavelength scanning fiber laser light source according to claim 6, wherein the wavelength scanning fiber laser light source is calibrated.

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